Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Hannah LS on 03/01/2019 10:19:30
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Dan says:
My 6 year old son asked me would we all float into space if the Earth stopped spinning. I thought that gravity would stop that from happening. Is that right? And what would happen if it did stop spinning?
What do you think?
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The only effect on gravity would be that you would weigh slightly more on the equator than you do now but with no spin the weather would be much affected .
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Dan says:
My 6 year old son asked me would we all float into space if the Earth stopped spinning. I thought that gravity would stop that from happening. Is that right? And what would happen if it did stop spinning?
What do you think?
Floating away happens if you spin too fast. That would happen if Earth went around about 15 times faster than it does now, and chunks of the Earth would float away along with the people.
If spinning stopped, the sun would shine on only one side, and it would get hot enough there to boil away all water and cook all the creatures. The dark side would get so cold that even the air would freeze and fall like snow onto the ground.
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Dan says:
My 6 year old son asked me would we all float into space if the Earth stopped spinning. I thought that gravity would stop that from happening. Is that right? And what would happen if it did stop spinning?
What do you think?
Floating away happens if you spin too fast. That would happen if Earth went around about 15 times faster than it does now, and chunks of the Earth would float away along with the people.
15 times wouldn't quite do it, even at the equator. Tangential speed at the equator is ~464 m/sec. 15 times that is 6960 m/sec. Orbital velocity at the equator is ~7606 m/sec. So it takes about a 17 times increase to get someone at the equator to just float above the ground. To fling them away from Earth, never to return, would require the rotation to increase to 24 times. And since the tangential velocity decreases as you move away from the equator to the poles, it takes even greater rotation rates to create the same effect at higher latitudes.
If spinning stopped, the sun would shine on only one side, and it would get hot enough there to boil away all water and cook all the creatures. The dark side would get so cold that even the air would freeze and fall like snow onto the ground.
If the Earth completely stopped it rotation, then its orientation would remain constant with respect to the "fixed" stars. Since assume it would still be orbiting the Sun, we would still have a day/night cycle, it would just be a year long.
The situation you describe is more like a tidally locked planet, which has had its rotational period locked to the be the same as its orbital period.
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if the Earth stopped spinning
We know of no power that would stop the Earth spinning, short of a similar-sized planet smashing into it. This would melt the entire crust, boil the oceans and blast away the atmosphere, incinerating the entire population. But some of your ashes might be blown away into space...
But let's imagine that the rocky Earth suddenly stopped spinning, plus the trees and buildings attached to it. We would suddenly find ourselves traveling at a fair fraction of the speed of sound into the nearest wall/tree/mountain, etc. Those away from any nearby objects would find themselves with a severe case of gravel rash. Only people at the North and South Poles would avoid this immediate death.
Once all the mayhem subsided, we would find ourselves still firmly attached to the Earth by its gravity.
- The Earth's oceans and atmosphere would settle into a spherical shape, not their current ellipsoidal shape
- But rocks take a lot longer to ooze into new shapes, so they would retain their original ellipsoidal shape for a million years or so, gradually moving into a more spherical shape, accompanied by heightened earthquake activity
- Initially, Earth's equatorial bulge would cause today's equatorial continents to project through much of the Earth's atmosphere. Much of today's equatorial seafloor would be dry.
- The ocean will flood to the poles, flooding most polar and many temperate countries, and drowning those who escaped the gravel rash
So if the Earth suddenly ceased spinning, it would cause major catastrophic changes on the Earth, but floating off into space would not be one of them.
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Floating away happens if you spin too fast. That would happen if Earth went around about 15 times faster than it does now, and chunks of the Earth would float away along with the people.
15 times wouldn't quite do it, even at the equator. Tangential speed at the equator is ~464 m/sec. 15 times that is 6960 m/sec. Orbital velocity at the equator is ~7606 m/sec. So it takes about a 17 times increase to get someone at the equator to just float above the ground.
I figured 16, but knocked one off. At 15x speed, the equatorial bulge would be so great that the speed of the new equator would be enough for orbital speed. Somewhere they must have computed the max speed for Earth spin before it flies apart like that, and I bet it is quite a bit less than 15x. One theory competing with Theia-origin of the moon was that Earth simply spun it off in this fashion, no collision required.
Anyway, 15x rotation with an equatorial bulge appropriate to that speed would be an object with more angular momentum than a sphere spinning at 17x our angular rate. It's going to fly apart.
To fling them away from Earth, never to return, would require the rotation to increase to 24 times. And since the tangential velocity decreases as you move away from the equator to the poles, it takes even greater rotation rates to create the same effect at higher latitudes.
I hadn't expected escape velocity. OK, so you spin the thing up to say 20x and Earth flies apart, but it all stays in orbit, leaving a smaller core behind. What happens to all that stuff? Does it congeal into a new moon? A bunch of them? Surely a bunch at first, but all the big pieces clean up the little ones in not much time, and then combine into probably a binary planet sort of like Pluto and Charon (which are not one separated body).
If the Earth completely stopped it rotation, then its orientation would remain constant with respect to the "fixed" stars. Since assume it would still be orbiting the Sun, we would still have a day/night cycle, it would just be a year long.
Indeed. But 6 months seems long enough to repeatedly boil off the dawn and freeze it all again at dusk.
Maybe not. The poles hardly get cold enough to freeze anything but the water despite the 6 dark months. Heat convects up there to prevent that, just like it does on the dark side of Venus, which is dark for a bloody long stretch each 'day'.
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https://io9.gizmodo.com/xkcds-creator-explains-what-would-happen-if-earth-stopp-1625068208